At 10,000m (or 33,000ft) of altitude, a human has a useful consciousness of about 20-30 seconds and will survive for just a few minutes.
This was the stark warning given to French skydivers Fred Fugen and Vince Reffet before they embarked on their ambitious attempt to combine a high altitude jump with freefall acrobatics, followed by a proximity swoop over mountain ridges.
The video above gives the full background to their amazing adventure.
"When we started, my first objective was to make them aware of the dangers," says Dr Ryan Jackson, their high altitude advisor.
As can be imagined, the project required considerable logistical planning and support. But one of the biggest obstacles was not the lack of oxygen but the strict regulations imposed by air traffic controllers in Geneva.
Technically it was very difficult
"They only gave us a window of between 3pm and 3.15pm to make the jump, as we were in the middle of the airspace for all the commercial airline traffic," says Fred.
"The problem was the turbulence. In the afternoon, it's much more powerful and it was a real challenge to go down the mountains and stay close to the rocks without losing control. Technically, it was very difficult."
"The project was the result of a lot of prepartion," he adds. "It was a big dream and I'm so happy we made it."
Besides the back up team, Fred and Vince were joined by Texan cameraman Noah Bahnson.
"He did the same jump as us but with a camera and a still camera on his head!" says Fred.
Go show your respect, by watching his results here!